Charge-trapping type flash memory devices are being widely applied in various fields such as mobile telecommunication systems and memory cards. One type of charge-trapping type flash memory device includes a stacked gate structure obtained by sequentially stacking a tunneling oxide film, a charge storing layer, a blocking oxide film and a gate electrode on a semiconductor substrate. The tunneling oxide film can contact source/drains composed of impurity regions formed in the semiconductor substrate. Also, the charge storing layer can include a trap site which stores charges passing through the tunneling oxide film. The blocking oxide film can prevent/reduce leakage of the electrons to the gate electrode when they are trapped at the trap site in the charge storing layer and may prevent/reduces intrusion of the charges of the gate electrode into the charge storing layer when they are trapped at the trap site in the charge storing layer.
In the charge-trapping type flash memory device constructed as above, the electrons having passed through the tunneling oxide film by a voltage supply can be trapped at the trap site in the charge storing layer. In the charge-trapping type nonvolatile semiconductor memory device, the threshold voltage Vth may vary based on whether the electrons are trapped in the charge storing layer or not.